The present invention relates to a fuel injector.
Fuel injectors in which swirl-producing elements are incorporated into a valve-seat member are referred to in German Patent No. 41 31 499. The swirl-producing element is implemented in the form of grooves which are incorporated into the valve-seat member and discharge into an injection orifice. The metering of the volume of fuel to be injected is accomplished by the cross section of the injection orifice. The injection orifice is located either in the valve-seat member or in a perforated disk which is situated at the downstream end of the fuel injector.
An additional fuel injector in which the swirl is produced by grooves is referred to in German Patent No. 42 31 448. The swirl-producing elements are located upstream from the sealing seat and are incorporated in the form of grooves in a central recess of the valve-seat member which is used to guide the valve-closure member. The swirl grooves, which are open toward the center line of the fuel injector, are closed by the valve-closure member, which is spherical, to form channels. This defines a cross section within the swirl channels through which the fuel is metered.
One disadvantage of the fuel injector referred to in German Patent No. 41 31 499 is the position of the swirl-creating element downstream from the sealing seat. The danger of contamination from coking is great, especially in the case of directly injecting fuel injectors. Particular attention must paid in the configuration to ruggedness of the swirl-producing elements; this limits the configuration options for the component, since minimum requirements for material thickness for example must be adhered to.
A further disadvantage is that the location downstream from the sealing seat causes a dead volume to be formed, from which fuel may escape after the injection operation ends. This afterdripping results in incomplete and uncontrolled combustion, which produces a large amount of pollutants. In addition, the one-piece configuration of nozzle body and valve-seat member makes it difficult to produce the grooves. Exceeding of component tolerances which may occur during manufacturing thus result in the rejection of an expensive component.
In the fuel injector referred to in German Patent No. 42 31 448, completing the grooves into swirl channels by the spherical valve-closure member is disadvantageous. The spherical geometry of the valve-closure member causes the swirl grooves to be closed to form swirl channels only at the circumference of the valve-closure member. This makes it difficult to prevent leakage, since the tolerances of several components are cumulative. This is particularly critically apparent because the sealing gap is in the form of a line. The result is a wide range of variation in the metered fuel volume.
Also disadvantageous is the necessary strong deflection of the fuel stream. This results from the arrangement of the swirl channels on the cylindrical wall of the recess which guides the valve-closure member. The adjacent swirl chamber is necessary to produce a uniformly turbulent stream. However, the associated deflection of the stream leads to severe losses of flow, which are evident in a poorer injection pattern. In addition, during the process of opening the fuel injector a pre-jet is formed, which includes no swirl. The resulting poor atomization causes deficient combustion.
The exemplary fuel injector according to the present invention may provide that the swirling fuel stream reaches the injection orifice without strong deflection. At the same time the swirl-producing elements are in a protected arrangement upstream from the sealing seat. The separation of the swirl production from the metering of the fuel to be injected is a further advantage for manufacturing. Relatively rough dimensional tolerances may be chosen for the swirl-producing elements, this may allow the use of more economical production methods.
Adaptation of the fuel injector to customer requirements in regard to the volume of fuel to be injected and injection pattern is simple. This is done by modifying only one component, which is able to influence both the swirl production and fuel metering. The swirl production may be varied by influencing the axial component of the fuel stream. This results in modification of the envelope of the cone on which the fuel is injected.
The metered volume is also adjusted while retaining the valve-seat member unchanged, by modifying an annular gap which is produced by an offset in the valve-closure member. In addition to the definition of a metered volume with the fuel injector completely open, the opening and closing response may be influenced by modifying the contour of the offset.
A further advantage is an arrangement of the swirl channels on a cone envelope whose angle is identical to the angle of the valve seat surface. Because of the resulting elimination of strong flow deflection downstream from the production of the swirl there is no loss in circumferential speed of the fuel on the way to the injection orifice.
This results in the further advantage of the elimination of a dead volume downstream from the production of swirl. Consequently a swirl is formed in the fuel stream as early as during the process of opening the fuel injector. In the final analysis, the improved swirl conditioning during opening and closing ensures improved combustion and thus results in lower emission of pollutants.